The present invention generally relates to the field of programming semiconductor, and more specifically, to a method and an apparatus for selectively programming a semiconductor device via the removal of conductive links (fuses).
The use of fusible links for redundancy programming of semiconductor devices (e.g. DRAMs. and SKAM""s, and embedded arrays in various logic dies) is a well known technique. Fusible links are also used to create electronic identification and serial numbers on dies. and to program dies for different functions, or to trim devices for ranges of operation. The most common method of blowing (removing) these links is by laser oblation. One example of such a fusible link for laser oblation is described in U.S. Pat. No. 5,760,674 to Gilmour et al.
A reason for the popularity of fuse blowing techniques, is that the techniques are readily applicable to devices, single dies, and wafers full of dies. Further, the current techniques also provide the ability to uniquely program each die. The use of laser fuse blow techniques also allows the fast selection of the fuses to be blown from among the numerous fuses residing in a set on a single die. Typical laser fuse blow techniques are driven by computer in order to allow individual fuse blow patterns on each die of a wafer.
There are problems, however, with the laser blow technique when the metallurgy of the device or fusible link is copper and/or the dielectric isolation is a porous material of the class of materials known as low dielectric constant dielectrics. or low k dielectrics. Copper is typically used to lower the resistance of signal lines, while low k dielectrics are often used to reduce the capacitive coupling between signal lines. Both of these effects are desirable, since they improve overall device performance.
Lasers blow fuses by heating up the link to the point where it boils and literally ejects material under high pressure. Traditionally, the metal of the fuse has been aluminum. If copper is used as the fuse material, the higher laser power is required, increasing the risk of damage to the dielectric isolation. Other effects of laser oblation of fuses on devices using low k dielectrics are: 1) the porous cell structure low k dielectric will collapse and electrically degrade the chip performance and, 2) injection into and subsequent migration within the porous low k dielectric of metal atoms expelled from the link during fuse blow.
It would be, therefore, a distinct advantage to have a technique for blowing fuses residing on low k dielectrics that would allow fast selection of the fuses to be blown, and unique programming of fuse blows for a set on a die. The present invention provides such a method and apparatus.
The present invention provides a method of programming a semiconductor device using photolithographic means by forming a layer of photoresist over an array of conductive links; removing a pre-selected portion of the photoresist from a subset of said array of conductive links; and removing the thus exposed conductive links.
The present invention further provides a method of programming a semiconductor wafer having dies with each die having arrays of conductive links, comprising the steps of:
(a) forming a layer of photoresist on the wafer;
(b) aligning and opening a pre-selected portion of shutters in the shutter array corresponding to a programming pattern;
(c) exposing the photoresist to activating illumination through the shutter array;
(d) repeating steps b-d for each of the remaining dies on said wafer; and
(e) developing the photoresist layer and removing unprotected conductive links.
The present invention also provides a system for programming semiconductor dies on a wafer coated with photoresist, each die having an array of conductive links, comprising:
testing each die on the wafer to determine which conductive links to remove;
creating a wafer test data set based on an electrical location of each conductive link to be removed;
converting said electrical location of each conductive link to be removed in the wafer test data set to a physical location of each conductive link to be removed that is stored in a link removal data set; and
converting the link removal data set to shutter and stage control data sets suitable for use by a lithographic exposure system having an array shutter system and a stage alignment system, wherein the lithographic exposure system uses the stage control data set to align each die to said array shutter system and uses the shutter control data set to open array shutter elements corresponding to conductive links to be removed.